Telephone station sets are generally interconnected by two or more wires to either a central office or other exchange such as a private business exchange or local switching controller. With a common battery type system direct current is supplied by the central office or exchange to the telephone station set over a tip and ring pair. In addition, the tip and ring pair is normally used to carry voice communications, dialing, ringing signals and switchhook supervision between the telephone station set and central office or exchange. A typical telephone circuit arrangement used to provide these functions is shown in FIG. 2 of U.S. Pat. No. 2,629,783 issued to H. F. Hopkins on Feb. 24, 1953.
If a visual indicating capability is required on the telephone, an arrangement such as disclosed in U.S. Pat. No. 3,322,903 issued to D. M. Chapin on May 30, 1967 may be implemented. Other telephone arrangements such as the 500Y station set manufactured by Western Electric Company utilize three wires to connect the telephone station set to a central office or exchange. In the 500Y station set the tip and ring leads carry voice communications, dialing, switchhook supervision and visual signaling. The ringing signal for the 500Y station set is carried between the third wire and the ring lead.
To improve the longitudinal balance and quality of voice communications some modern telephone switching controllers require isolation of the voice communication path from the switchhook supervision, ringing and visual signaling path. However, it is also an objective in such applications to minimize the number of wire pairs needed to provide the various signaling requirements to the connected telephones.
In U.S. Pat. No. 3,453,396 issued on July 1, 1969 to J. C. Lacey et al, voice communications and ringing are provided on a tip and ring pair with supervision and visual indications being provided by a second pair. In Lacey the pickup key of a key telephone is used to provide a lamp current reversal for A lead signaling. The Lacey patent, however, does not provide for isolation of the voice communications from the switchhook supervision, ringing and visual signaling.
In U.S. Pat. No. 4,046,972 issued on Sept. 6, 1977 to D. D. Huizinga et al an electronic key telephone station set is described which communicates with a telephone controller using a data transmit pair and a data receive pair for data communications in addition to a tip and ring pair for voice communications. In Huizinga, digital data signals representative of the switchhook supervision, ringing, visual and other signals are sent over the data transmit and data receive pairs. Digital multiplex data signaling is utilized in Huizinga which enables multiple telephone line signaling over the data transmit and data receive pairs.
In applications involving existing telephone controllers (telephone systems), it may be desirable to utilize the signaling voltages available at the telephone controller to provide the switchhook supervision, ringing and visual signaling for telephone operation. In these applications a telephone station set is required which both utilizes the available signaling voltages from the telephone controllers, as well as maintaining the desired isolation of voice communication from the signaling voltages. Neither Huizinga nor the previously mentioned telephone station set prior art communicate voice signals over a first wire pair and communicate existing signaling voltages over a second wire pair.
Thus, one objective is to design a telephone station set which provides voice communications and dialing over one wire pair and switchhook supervision, ringing and visual signaling over a second wire pair.
Another objective is to utilize the existing signaling voltages available at the telephone switching controllers to provide the required signaling to the telephone station set.
A further objective is to minimize the modifications required to a standard telephone station set to perform the desired signaling functions.